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Combined de-inking technology applied on laser printed paper
Chemical Engineering and Processing 48 (2009) 587–591
Contents lists available at ScienceDirect
Chemical Engineering and Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep
Combined de-inking technology applied on laser printed paper Sui Zhenying a , Dong Shijin a , Cui Xuejun a , Gao Yan a , Li Junfeng a , Wang Hongyan a,∗ , Sean X. Zhang b a b
College of Chemistry, Jilin University, Changchun 130012, China HP Labs, Hewlett-Packard Company, Palo Alto, CA, 95014, USA
a r t i c l e
i n f o
Article history: Received 18 December 2007 Received in revised form 27 June 2008 Accepted 27 June 2008 Available online 9 July 2008 Keywords: Laser printed paper Enzymes Ultrasonic UV irradiation Combined de-inking technology
a b s t r a c t The combined de-inking technology of ultrasonic, UV irradiation and enzymatic methods was introduced into the de-inking process of HP laser printed paper. The purpose was to reduce the consumption of alkali or even preprocess without alkali absolutely for the purpose of environment protection. The deinking effects of cellulase, amylase, lipase and their mixture were compared and the experiment results showed that combined enzymes of cellulase and amylase have the best de-inking efficiency which has a 12% increment of brightness. The de-inking efficiencies of several different de-inking technologies were compared, which can provide basis to establish combined de-inking technologies. © 2008 Elsevier B.V. All rights reserved.
1. Introduction With the rapid development of office automation and information, the proportion of laser printed paper in the consumption of office paper has been increasing day after day [1]. People pay more attention to recycle of waste paper for the protection of forest resources and environment. Paper mill will gain profit from the utilization of recycled fiber, it is profitable to decrease pollution, cost, and investment. Therefore, waste paper recycling is becoming one of the top topics all over the world. Laser printing toner is made of carbon black, thermoplastic resins and electric–magnetic iron oxide. The thermoplastic resins that we commonly use are polystyrene, the copolymerization of ethylene and vinyl acetate, nitro cellulose, polyvinyl chloride (PVC), polyamide (PA) and polyester, etc. [2]. The resins in the toner are melted and adhered with carbon black on the paper in printing process. Conventional de-inking technology with alkali cannot get great efficiency to laser printed paper and has threatened environment badly. Consequently, experts paid more and more attention to new de-inking technologies [3,4]. The research of bio-de-inking technology has opened up a new way for paper de-inking [5–13]. Besides,
ultrasonic and other technologies have begun to be investigated by some researchers, which is still in its starting stage. On the basis of the conventional de-inking technology, the combined de-inking technology with ultrasonic, UV irradiation and enzymes was investigated in this paper. We have researched the impact factors of de-inking process in detail in order to find out the proper operating parameters of combined de-inking technology for HP laser printed paper. 2. Experimental 2.1. Chemicals Cellulase and amylase were purchased from Shanghai Chemicals Company, China. Enzyme activity of cellulase was 15,000 U/g and enzyme activity of amylase was 2000 U/g. Sodium dodecyl benzene sulfonate (SDBS) was purchased from Tianjin Chemicals Company, China. Sodium hydroxide was purchased from Fine Chemicals Limited Company of Chemical Engineering University in Beijing, China. All chemicals were of analytical grade. 2.2. Material
∗ Corresponding author at: Qianjin Street 2699, Department of Applied Chemistry, College of Chemistry, Jilin University, Changchun 130012, China. Tel.: +86 431 85168470; fax: +86 431 85168470/71. E-mail address: wang [email protected] (W. Hongyan). 0255-2701/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cep.2008.06.014
The material used was laser printed paper, obtained from HP 5L/6L. Laser printed paper was crushed into small pieces and soaked at room temperature for 18 h.
588
S. Zhenying et al. / Chemical Engineering and Processing 48 (2009) 587–591
2.3. Instruments Flotation experiments were carried out using the XFD single trough device (1.5 L). Ultrasonic experiments were carried out using the KQ3200E ultrasonic cleaning device (40 kHz, 6 L, 120 W). UV irradiation experiments were carried out using SL-1 UV box (1000 W). Brightness measuring experiments were carried out using the WSB-3 digital brightness meter. Dirt area measuring experiments were carried out using the computer software made by College of Chemistry, Jilin University. All instruments were made in China. 2.4. Technologies (a) Direct enzymatic de-inking Waste paper → water soak → dispersing → enzymatic treatment → flotation → filtration → drying → brightness measuring (b) Enzymatic de-inking with alkali preprocessing before dispersing Waste paper → alkali soak → dispersing → enzymatic treatment → flotation → filtration → drying → brightness and dirt area measuring (c) Enzymatic and ultrasonic processing de-inking Waste paper → water soak → dispersing → enzymatic treatment → ultrasonic treatment → flotation → filtration → drying → brightness and dirt area measuring (d) Enzymatic and UV irradiation processing de-inking Waste paper → UV irradiation → enzymatic process → flotation → filtration → drying → brightness and dirt area measuring Above technologies were explained using following: • Waste paper—the waste paper used in experiment was laser printed paper from HP 5L/6L. • Water soak—8 g (dry basis) of laser printed paper for each sample was crushed into small pieces by cutting machine and immersed into water at room temperature for 18 h. • Dispersing—prior to enzymatic treatment, the pulp samples were disintegrated in disintegrator at 3000 r/min for 30 min. The temperature was 20 ◦ C. • Enzymatic treatment—the enzyme treatments of pulp were carried out using cellulase and amylase at 40 ◦ C for 30 min. Cellulase and amylase concentrations (w/w) see conditions of following Tables 1–4 and Figs. 1 and 2. • Alkali soak—0.4% (w/w) NaOH based on the weight of fiber was used to soak the pulp. • Ultrasonic treatment—the pulp samples were treatment for 20 min in the KQ3200E ultrasonic cleaning device. • UV irradiation—laser printed paper was irradiate for 1 min in SL-1 UV box. • Flotation—the pulp samples were diluted to 1% consistency using water. All flotation experiments were performed in XFD flotation device of single trough (1.5 L) at room temperature, 0.8 g of sodium dodecyl benzene sulfonate (SDBS) was used as surfactants. During the flotation, pressure was 101.325 kPa, the airflow set to 0.064 m3 /h, and the foam with toner particles was continually skimmed away from the cell surface. • Filtration—after flotation, the pulp samples were washed by water and the de-inking fibers were made a hand sheet. • Drying—the hand sheet were placed on dry plates and dried at room temperature. • Brightness and dirt area measuring—brightness were measured three time at different places on each face, brightness are
expressed as the average value. Dirt area was measured using the computer software of dirt area. Dirt area was the percentage of the total dirt area and the total area scanned. 2.5. Results contrast In all the experiments, the effects of de-inking were compared with printed and non-treated paper. The printed and nontreated paper was controlled as following: waste paper → water soak → dispersing → filtration → drying → brightness and dirt area measuring. 3. Results and discussion 3.1. De-inking efficiency of different enzymes Cellulase, lipase, amylase and their mixture have been used in de-inking process. The mechanism of enzymatic de-inking is that the connection of toner and fibers are weakened when the enzymes attack toner particles and fibers, meanwhile toner particles separate from fibers [14,15]. HP laser printed paper has been investigated with different enzyme and their mixture according to Section 2.4 (Technology (a)). De-inking effects of various enzymes were compared with without enzymes and are shown in Fig. 1. Fig. 1 shows cellulase + amylase or cellulase + amylase + lipase can increase the brightness of paper pulp about 12%. For economical reason, we chose the mixture of cellulase and amylase as de-inking agents in all experiments. 3.2. Enzymes de-inking technology of alkali In conventional chemical de-inking technology, the pulp pH is 13–14. Toner particles are easily removed from fibers at the strong alkali condition. But the waste liquid of high pH is harmful to environment. We selected bio-de-inking technology and investigated the effect of pulp pH on enzymatic bio-de-inking according to Section 2.4 (Technology (b)). Results are shown in Table 1. Each kind of enzyme has a perfect pH to attain its highest activity. It can be easily seen from Table 1 that the brightness of pH 6–7* pulp is higher appreciably than that of pH 9–10 pulp, and their dirt area ratio is the same. But pH 6–7* pulp need to be adjusted from pH 9–10 to pH 6–7 before enzyme action. So it indicates that pH 9–10 pulp is suitable for enzymatic and alkali combined de-inking because of its convenience. At this condition, the contact of tiny fiber with alkaline solution will weaken the hydrogen bonding among tiny fibers and form single fiber which
Fig. 1. Effect of various enzymes. (1) Without enzymes; (2) 0.1% amylase; (3) 0.05% cellulase; (4) 0.05% cellulase + 0.1% amylase; (5) 0.05% cellulase + 0.17% lipase; (6) 0.05% cellulase + 0.1% amylase + 0.17% lipase. Reaction conditions: Pulp concentration was ≤6%; enzymatic processing time was 30 min; enzymatic temperature was 40 ◦ C; flotation time was 10 min.
S. Zhenying et al. / Chemical Engineering and Processing 48 (2009) 587–591
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Table 1 Influence of pH on enzymatic de-inking Pulp pH
Brightness (%ISO)
Average (%ISO)
Dirt area (%)
6–7
67.00 67.00
66.31 67.00
65.30 67.00
67.00 66.35
67.02 67.00
67.00 66.18
66.68
0.31
9–10
67.00 66.67
67.89 67.00
67.93 67.00
67.00 67.00
66.95 67.55
67.00 67.00
67.17
0.08
6–7*
67.75 69.03
67.75 69.03
68.16 69.03
68.49 68.48
68.49 69.03
67.94 69.17
68.10
0.08
13–14
64.64 67.00
66.98 65.97
66.95 65.40
64.63 65.58
67.00 67.00
67.54 67.46
66.35
0.15
Printed and non-treated paper brightness (%ISO) Printed and non-treated paper dirt area (%)
62.35 0.60
Conditions: Alkali concentration 0.4% (w/w); alkali processing time 45 min; alkali processing temperature 60 ◦ C; pulp concentration 4% (w/w); mixture of cellulase and amylase processing time 30 min; enzymes processing temperature 40 ◦ C; the cellulase concentration of 0.1% (w/w) was selected for treating 8 g of dry pulp sample; the amylase concentration of 0.14% (w/w) was selected for treating 8 g of dry pulp sample; printed and non-treated papers sample was the pulp sample not treated with enzyme and also not processed by alkali and flotation. * Firstly alkali pre-treating was carried out at pH 9–10, and then the pulp pH was adjusted to 6–7 for enzymatic process.
Table 2 Combined de-inking of ultrasonic and enzymatic Sample
Un-ultrasonic
Cellulase + amylase Control pulp
Ultrasonic
Brightness (%ISO)
Dirt area (%)
Brightness (%ISO)
Dirt area (%)
76.10 68.89
0.28 0.56
77.41 69.26
0.23 0.42
Printed and non-treated paper brightness (%ISO) Printed and non-treated paper dirt area (%)
68.47 0.48
Conditions: Ultrasonic processing time 20 min; ultrasonic processing temperature 40 ◦ C; enzymatic processing time 30 min; enzymatic processing temperature 40 ◦ C; the cellulase concentration of 0.05% (w/w) was selected for treating 8 g of dry pulp sample; the amylase concentration of 0.1% (w/w) was selected for treating 8 g of dry pulp sample; printed and non-treated papers sample was the pulp sample not treated with enzymes and also not processed by ultrasonic and flotation; Control pulp was taken under similar conditions but not treated with enzymes.
can favor the toner loosening and the toner particles can be easily departed from fibers. Besides, the condition of pH 9–10 de-inking can decrease the environment pollution as compared to traditional methods.
the surface of fiber. This is favorable for the removal of toner particles. In order to obtain optimal de-inking effect, under experiment conditions same as Table 2. HP laser printed paper has been investigated with the mixture of cellulase and amylase according to Section 2.4 (Technology (c)). The influences of different ultrasonic time on the de-inking effect were investigated (see Table 3). Table 3 shows the brightness decreases and dirt area increases with the extending of ultrasonic processing time. 5 min ultrasonic time is suitable. It can be explained that ultrasonic processing can peel off toner from fibers very effectively. But the peeled toner maybe become thinner with prolonging of ultrasonic time, the toners have more chance to redeposit on the surface of fibers. Therefore the brightness continuously falls, and the dirt area goes on ascending.
3.3. Combined de-inking technology of ultrasonic and enzymes The paper by HP laser printed has been investigated with the mixture of cellulase and amylase according to Section 2.4 (Technologies (a) and (c)). The results of de-inking technology are shown in Table 2. Table 2 shows that the brightness of the combined de-inking of ultrasonic and enzymatic is slightly higher than the brightness of cellulase + amylase while the dirt area is comparatively lower. But their brightness is much higher than control pulp and their dirt area are much lower than control pulp. Therefore combined de-inking technology with ultrasonic and enzymes can improve the brightness successfully and dirt area of pulp to some degree. The reason is that ultrasonic can produce periodically expansion and compression which will cause the vibration and friction between fibers, quicken the hydrolysis rate of carbon hydrate on
3.4. Combined de-inking technology of UV irradiation and enzymes Laser printing toner contains some thermosetting resin which can be solidified while printing. The solidified resin can make the
Table 3 Influence of different ultrasonic processing time Time (min)
Brightness (%ISO)
5 10 15 20
72.74 72.38 70.86 70.77
Printed and non-treated paper brightness (%ISO) Printed and non-treated paper dirt area (%)
72.43 72.74 71.86 71.23
72.60 72.42 71.86 70.68
72.74 72.62 70.58 70.30
72.38 72.74 71.86 70.70 62.35 0.60
72.54 72.38 71.76 71.74
Average (%ISO)
Dirt area (%)
72.57 72.55 71.46 70.90
0.22 0.32 0.38 0.52
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S. Zhenying et al. / Chemical Engineering and Processing 48 (2009) 587–591
Table 4 De-inking effect of combined de-inking technology of UV irradiation and enzymes Technology
Brightness (%ISO)
Cellulase + amylase UV + mixture of enzymes
69.11 69.09
68.37 68.55
68.21 70.45
68.22 72.40
Printed and non-treated paper brightness (%ISO) Printed and non-treated paper dirt area (%)
68.89 71.41
68.22 71.44
Average (%ISO)
Dirt area (%)
68.50 70.56
0.38 0.02
62.35 0.60
Conditions: enzymes processing time 30 min; enzymes temperature 40 ◦ C; UV time 1 min; pulp concentration 4% (w/w); the cellulase concentration of 0.06% (w/w) was selected for treating 8 g of dry pulp sample; the amylase concentration of 0.088% (w/w) was selected for treating 8 g of dry pulp sample; printed and non-treated papers sample was the pulp sample not treated with enzyme and also not processed by UV and flotation.
particles very difficult to be peeled off from fibers. Therefore, it is a problem desiderated to be solved in de-inking technology. UV can initiate degradation of polymers or even break it into pulverization. For this reason, the actions of laser printing paper irradiated by ultraviolet have been investigated (see Figs. 2 and 3 and Table 4). According to Section 2.4 (Technology (d)), the combine deinking technology of UV radiation and mixture of enzymes was experimented and compared it with mixture enzymes de-inking technology. Table 4 shows UV can improve brightness of pulp in some degree and reduce dirt area obviously. From Fig. 2, we can see when irradiation time is 0–1 min by 1000 W UV lamp, brightness rise and dirt area descend. The reason may be that thermosetting resin is partly decomposed by UV irradiation which makes the particles loosen, and then the toner particles are easy to be removed during flotation and water washing. Brightness fall gradually and the change of dirt area is little when irradiation time is 2–5 min. The phenomenon can be explained by the reason that paper becomes yellow with the time increasing of UV irradiation. Therefore considering brightness and dirt area, the appropriate UV irradiation time is 1 min or lower than 1 min. For observing the breakage action of ultraviolet irradiation to printed paper, big toner points were printed on the paper and they were irradiated by ultraviolet for different time respectively (see Fig. 3). From Fig. 3, we can see that the toner on fibers was distinctly tilted when irradiation time changed from 1 min (enclosing part of Fig. 3a), 2 min (Fig. 3b) to 4 min (Fig. 3c). It indicates ultraviolet irradiation is useful for de-inking. Otherwise, from Section 2.4 (Technology (d)), we know that the combined de-inking technology of UV irradiation and enzymes does not needed the preprocess with alkali, therefore, it is a environment-friendly de-inking technology.
Fig. 3. Photos of scanning electron microscopy (SEM) of different irradiation time.
Fig. 2. Influence of UV irradiation time on brightness and dirt area. Conditions: enzymes processing time 30 min; enzyme processing temperature 40 ◦ C; pulp mass concentration 4% (w/w); the cellulase concentration of 0.06% (w/w) was selected for treating 8 g of dry pulp sample; the amylase concentration of 0.088% (w/w) was selected for treating 8 g of dry pulp sample.
4. Conclusion The effect of combined de-inking technology of ultrasonic, UV irradiation and enzyme on HP laser printed paper has been investi-
S. Zhenying et al. / Chemical Engineering and Processing 48 (2009) 587–591
gated. The results indicate that the dose of alkali can be reduced using combined de-inking technology. A combined technology of simple, economical and environment-friendly can be achieved using ultrasonic, UV irradiation, and enzyme operation. Acknowledgment The authors greatly appreciate the support of Hewlett-Packard (HP) Company. References [1] Wu Shufang, Ding Shaojun, Li Zhongzheng, Function of endocellulase in the deinking process of mixed office waste paper, Chem. Ind. Forest Prod. 25 (2005) 87–90. [2] Fu Yingjuan, Qin Menghua, Hu Huiren, Effect of types and properties on the deinkability of wastepaper, Trans. Chin. Pulp Paper 20 (2005) 155–159. [3] Li Zongquan, Qin Menghua, Zhan Huaiyu, Enzymatic deinking of mixed office waste, Paper Sci. Technol. 22 (2003) 7–10. [4] Hu Zhanbo, Wang Shuangfei, Liang Dongmei, Cellulase enzymatic deinking of mixed office waste, Paper Sci. Technol. 22 (2003) 11–16. [5] U. Viestur, M. Leite, M. Eisimonte, T. Eremeewa, A. Treimanis, Biological deinking technology for the recycling of waste papers, Bioresour. Technol. 67 (1999) 255–267.
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[6] S. Marques, H. Pala, L. Alves, M.T. Amaral-Collaco, F.M. Gama, F.M. Girio, Characterization and application of glycanases secreted by Aspergillus terreus CCMI 498 and Trichoderma viride CCMI 84 for enzymatic deinking of mixed office waste papers, J. Biotechnol. 100 (2003) 200–219. [7] S. Vyas, A. Lachke, Biodeinking of mixed office waste paper by alkaline active cellulases from alkalotolerant Fusarium sp., Enzyme Microb. Technol. 32 (2003) 236–245. [8] H. Pala, M.A. Lemos, M. Mota, F.M. Gama, Enzymatic upgrade of old paperboard containers, Enzyme Microb. Technol. 29 (2001) 274–279. [9] N.E. Franks, N. Munk, Alkaline cellulase and enzymatic de-inking of mixed office waste, Proc. Tappi Conf. (1995) 343–347. [10] T.W. Jeffries, L.H. Klungness, M.H. Sykes, C.K.R. Rutledge, Comparison of enzyme enhanced with conventional de-inking of xerographic and laser printed waste papers, Tappi J. 77 (1994) 173–179. [11] A.L. Morbak, W. Zimmermann, De-inking of mixed office paper, old newspaper and vegetable oil based ink printed paper using cellulase, xylanases and lipases, Progr. Paper Recycl. 7 (1998) 14–27. [12] K.H. Paik, J.Y. Park, Enzyme de-inking of newsprint waste (I)—Effect of cellulase and xylanase on brightness, yield and physical properties of deinked pulps, J. Kor. Tappi 25 (1993) 42–53. [13] U. Viestur, M. Leite, M. Eisimonte, T. Eremeewa, A. Treimanis, Biological deinking technology for the recycling of waste papers, Bioresour. Technol. 67 (1999) 255–267. [14] T. Moon, R. Nagarajan, Deinking of xerographic and laser-printed paper using block copolymers, Colloids Surf. A: Physiochem. Eng. Aspects 132 (1998) 275–288. [15] T. Welt, R. Dinus, Enzymatic deinking, Progr. Paper Recycl. 4 (1995) 36–47.
Contents lists available at ScienceDirect
Chemical Engineering and Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep
Combined de-inking technology applied on laser printed paper Sui Zhenying a , Dong Shijin a , Cui Xuejun a , Gao Yan a , Li Junfeng a , Wang Hongyan a,∗ , Sean X. Zhang b a b
College of Chemistry, Jilin University, Changchun 130012, China HP Labs, Hewlett-Packard Company, Palo Alto, CA, 95014, USA
a r t i c l e
i n f o
Article history: Received 18 December 2007 Received in revised form 27 June 2008 Accepted 27 June 2008 Available online 9 July 2008 Keywords: Laser printed paper Enzymes Ultrasonic UV irradiation Combined de-inking technology
a b s t r a c t The combined de-inking technology of ultrasonic, UV irradiation and enzymatic methods was introduced into the de-inking process of HP laser printed paper. The purpose was to reduce the consumption of alkali or even preprocess without alkali absolutely for the purpose of environment protection. The deinking effects of cellulase, amylase, lipase and their mixture were compared and the experiment results showed that combined enzymes of cellulase and amylase have the best de-inking efficiency which has a 12% increment of brightness. The de-inking efficiencies of several different de-inking technologies were compared, which can provide basis to establish combined de-inking technologies. © 2008 Elsevier B.V. All rights reserved.
1. Introduction With the rapid development of office automation and information, the proportion of laser printed paper in the consumption of office paper has been increasing day after day [1]. People pay more attention to recycle of waste paper for the protection of forest resources and environment. Paper mill will gain profit from the utilization of recycled fiber, it is profitable to decrease pollution, cost, and investment. Therefore, waste paper recycling is becoming one of the top topics all over the world. Laser printing toner is made of carbon black, thermoplastic resins and electric–magnetic iron oxide. The thermoplastic resins that we commonly use are polystyrene, the copolymerization of ethylene and vinyl acetate, nitro cellulose, polyvinyl chloride (PVC), polyamide (PA) and polyester, etc. [2]. The resins in the toner are melted and adhered with carbon black on the paper in printing process. Conventional de-inking technology with alkali cannot get great efficiency to laser printed paper and has threatened environment badly. Consequently, experts paid more and more attention to new de-inking technologies [3,4]. The research of bio-de-inking technology has opened up a new way for paper de-inking [5–13]. Besides,
ultrasonic and other technologies have begun to be investigated by some researchers, which is still in its starting stage. On the basis of the conventional de-inking technology, the combined de-inking technology with ultrasonic, UV irradiation and enzymes was investigated in this paper. We have researched the impact factors of de-inking process in detail in order to find out the proper operating parameters of combined de-inking technology for HP laser printed paper. 2. Experimental 2.1. Chemicals Cellulase and amylase were purchased from Shanghai Chemicals Company, China. Enzyme activity of cellulase was 15,000 U/g and enzyme activity of amylase was 2000 U/g. Sodium dodecyl benzene sulfonate (SDBS) was purchased from Tianjin Chemicals Company, China. Sodium hydroxide was purchased from Fine Chemicals Limited Company of Chemical Engineering University in Beijing, China. All chemicals were of analytical grade. 2.2. Material
∗ Corresponding author at: Qianjin Street 2699, Department of Applied Chemistry, College of Chemistry, Jilin University, Changchun 130012, China. Tel.: +86 431 85168470; fax: +86 431 85168470/71. E-mail address: wang [email protected] (W. Hongyan). 0255-2701/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cep.2008.06.014
The material used was laser printed paper, obtained from HP 5L/6L. Laser printed paper was crushed into small pieces and soaked at room temperature for 18 h.
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S. Zhenying et al. / Chemical Engineering and Processing 48 (2009) 587–591
2.3. Instruments Flotation experiments were carried out using the XFD single trough device (1.5 L). Ultrasonic experiments were carried out using the KQ3200E ultrasonic cleaning device (40 kHz, 6 L, 120 W). UV irradiation experiments were carried out using SL-1 UV box (1000 W). Brightness measuring experiments were carried out using the WSB-3 digital brightness meter. Dirt area measuring experiments were carried out using the computer software made by College of Chemistry, Jilin University. All instruments were made in China. 2.4. Technologies (a) Direct enzymatic de-inking Waste paper → water soak → dispersing → enzymatic treatment → flotation → filtration → drying → brightness measuring (b) Enzymatic de-inking with alkali preprocessing before dispersing Waste paper → alkali soak → dispersing → enzymatic treatment → flotation → filtration → drying → brightness and dirt area measuring (c) Enzymatic and ultrasonic processing de-inking Waste paper → water soak → dispersing → enzymatic treatment → ultrasonic treatment → flotation → filtration → drying → brightness and dirt area measuring (d) Enzymatic and UV irradiation processing de-inking Waste paper → UV irradiation → enzymatic process → flotation → filtration → drying → brightness and dirt area measuring Above technologies were explained using following: • Waste paper—the waste paper used in experiment was laser printed paper from HP 5L/6L. • Water soak—8 g (dry basis) of laser printed paper for each sample was crushed into small pieces by cutting machine and immersed into water at room temperature for 18 h. • Dispersing—prior to enzymatic treatment, the pulp samples were disintegrated in disintegrator at 3000 r/min for 30 min. The temperature was 20 ◦ C. • Enzymatic treatment—the enzyme treatments of pulp were carried out using cellulase and amylase at 40 ◦ C for 30 min. Cellulase and amylase concentrations (w/w) see conditions of following Tables 1–4 and Figs. 1 and 2. • Alkali soak—0.4% (w/w) NaOH based on the weight of fiber was used to soak the pulp. • Ultrasonic treatment—the pulp samples were treatment for 20 min in the KQ3200E ultrasonic cleaning device. • UV irradiation—laser printed paper was irradiate for 1 min in SL-1 UV box. • Flotation—the pulp samples were diluted to 1% consistency using water. All flotation experiments were performed in XFD flotation device of single trough (1.5 L) at room temperature, 0.8 g of sodium dodecyl benzene sulfonate (SDBS) was used as surfactants. During the flotation, pressure was 101.325 kPa, the airflow set to 0.064 m3 /h, and the foam with toner particles was continually skimmed away from the cell surface. • Filtration—after flotation, the pulp samples were washed by water and the de-inking fibers were made a hand sheet. • Drying—the hand sheet were placed on dry plates and dried at room temperature. • Brightness and dirt area measuring—brightness were measured three time at different places on each face, brightness are
expressed as the average value. Dirt area was measured using the computer software of dirt area. Dirt area was the percentage of the total dirt area and the total area scanned. 2.5. Results contrast In all the experiments, the effects of de-inking were compared with printed and non-treated paper. The printed and nontreated paper was controlled as following: waste paper → water soak → dispersing → filtration → drying → brightness and dirt area measuring. 3. Results and discussion 3.1. De-inking efficiency of different enzymes Cellulase, lipase, amylase and their mixture have been used in de-inking process. The mechanism of enzymatic de-inking is that the connection of toner and fibers are weakened when the enzymes attack toner particles and fibers, meanwhile toner particles separate from fibers [14,15]. HP laser printed paper has been investigated with different enzyme and their mixture according to Section 2.4 (Technology (a)). De-inking effects of various enzymes were compared with without enzymes and are shown in Fig. 1. Fig. 1 shows cellulase + amylase or cellulase + amylase + lipase can increase the brightness of paper pulp about 12%. For economical reason, we chose the mixture of cellulase and amylase as de-inking agents in all experiments. 3.2. Enzymes de-inking technology of alkali In conventional chemical de-inking technology, the pulp pH is 13–14. Toner particles are easily removed from fibers at the strong alkali condition. But the waste liquid of high pH is harmful to environment. We selected bio-de-inking technology and investigated the effect of pulp pH on enzymatic bio-de-inking according to Section 2.4 (Technology (b)). Results are shown in Table 1. Each kind of enzyme has a perfect pH to attain its highest activity. It can be easily seen from Table 1 that the brightness of pH 6–7* pulp is higher appreciably than that of pH 9–10 pulp, and their dirt area ratio is the same. But pH 6–7* pulp need to be adjusted from pH 9–10 to pH 6–7 before enzyme action. So it indicates that pH 9–10 pulp is suitable for enzymatic and alkali combined de-inking because of its convenience. At this condition, the contact of tiny fiber with alkaline solution will weaken the hydrogen bonding among tiny fibers and form single fiber which
Fig. 1. Effect of various enzymes. (1) Without enzymes; (2) 0.1% amylase; (3) 0.05% cellulase; (4) 0.05% cellulase + 0.1% amylase; (5) 0.05% cellulase + 0.17% lipase; (6) 0.05% cellulase + 0.1% amylase + 0.17% lipase. Reaction conditions: Pulp concentration was ≤6%; enzymatic processing time was 30 min; enzymatic temperature was 40 ◦ C; flotation time was 10 min.
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Table 1 Influence of pH on enzymatic de-inking Pulp pH
Brightness (%ISO)
Average (%ISO)
Dirt area (%)
6–7
67.00 67.00
66.31 67.00
65.30 67.00
67.00 66.35
67.02 67.00
67.00 66.18
66.68
0.31
9–10
67.00 66.67
67.89 67.00
67.93 67.00
67.00 67.00
66.95 67.55
67.00 67.00
67.17
0.08
6–7*
67.75 69.03
67.75 69.03
68.16 69.03
68.49 68.48
68.49 69.03
67.94 69.17
68.10
0.08
13–14
64.64 67.00
66.98 65.97
66.95 65.40
64.63 65.58
67.00 67.00
67.54 67.46
66.35
0.15
Printed and non-treated paper brightness (%ISO) Printed and non-treated paper dirt area (%)
62.35 0.60
Conditions: Alkali concentration 0.4% (w/w); alkali processing time 45 min; alkali processing temperature 60 ◦ C; pulp concentration 4% (w/w); mixture of cellulase and amylase processing time 30 min; enzymes processing temperature 40 ◦ C; the cellulase concentration of 0.1% (w/w) was selected for treating 8 g of dry pulp sample; the amylase concentration of 0.14% (w/w) was selected for treating 8 g of dry pulp sample; printed and non-treated papers sample was the pulp sample not treated with enzyme and also not processed by alkali and flotation. * Firstly alkali pre-treating was carried out at pH 9–10, and then the pulp pH was adjusted to 6–7 for enzymatic process.
Table 2 Combined de-inking of ultrasonic and enzymatic Sample
Un-ultrasonic
Cellulase + amylase Control pulp
Ultrasonic
Brightness (%ISO)
Dirt area (%)
Brightness (%ISO)
Dirt area (%)
76.10 68.89
0.28 0.56
77.41 69.26
0.23 0.42
Printed and non-treated paper brightness (%ISO) Printed and non-treated paper dirt area (%)
68.47 0.48
Conditions: Ultrasonic processing time 20 min; ultrasonic processing temperature 40 ◦ C; enzymatic processing time 30 min; enzymatic processing temperature 40 ◦ C; the cellulase concentration of 0.05% (w/w) was selected for treating 8 g of dry pulp sample; the amylase concentration of 0.1% (w/w) was selected for treating 8 g of dry pulp sample; printed and non-treated papers sample was the pulp sample not treated with enzymes and also not processed by ultrasonic and flotation; Control pulp was taken under similar conditions but not treated with enzymes.
can favor the toner loosening and the toner particles can be easily departed from fibers. Besides, the condition of pH 9–10 de-inking can decrease the environment pollution as compared to traditional methods.
the surface of fiber. This is favorable for the removal of toner particles. In order to obtain optimal de-inking effect, under experiment conditions same as Table 2. HP laser printed paper has been investigated with the mixture of cellulase and amylase according to Section 2.4 (Technology (c)). The influences of different ultrasonic time on the de-inking effect were investigated (see Table 3). Table 3 shows the brightness decreases and dirt area increases with the extending of ultrasonic processing time. 5 min ultrasonic time is suitable. It can be explained that ultrasonic processing can peel off toner from fibers very effectively. But the peeled toner maybe become thinner with prolonging of ultrasonic time, the toners have more chance to redeposit on the surface of fibers. Therefore the brightness continuously falls, and the dirt area goes on ascending.
3.3. Combined de-inking technology of ultrasonic and enzymes The paper by HP laser printed has been investigated with the mixture of cellulase and amylase according to Section 2.4 (Technologies (a) and (c)). The results of de-inking technology are shown in Table 2. Table 2 shows that the brightness of the combined de-inking of ultrasonic and enzymatic is slightly higher than the brightness of cellulase + amylase while the dirt area is comparatively lower. But their brightness is much higher than control pulp and their dirt area are much lower than control pulp. Therefore combined de-inking technology with ultrasonic and enzymes can improve the brightness successfully and dirt area of pulp to some degree. The reason is that ultrasonic can produce periodically expansion and compression which will cause the vibration and friction between fibers, quicken the hydrolysis rate of carbon hydrate on
3.4. Combined de-inking technology of UV irradiation and enzymes Laser printing toner contains some thermosetting resin which can be solidified while printing. The solidified resin can make the
Table 3 Influence of different ultrasonic processing time Time (min)
Brightness (%ISO)
5 10 15 20
72.74 72.38 70.86 70.77
Printed and non-treated paper brightness (%ISO) Printed and non-treated paper dirt area (%)
72.43 72.74 71.86 71.23
72.60 72.42 71.86 70.68
72.74 72.62 70.58 70.30
72.38 72.74 71.86 70.70 62.35 0.60
72.54 72.38 71.76 71.74
Average (%ISO)
Dirt area (%)
72.57 72.55 71.46 70.90
0.22 0.32 0.38 0.52
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Table 4 De-inking effect of combined de-inking technology of UV irradiation and enzymes Technology
Brightness (%ISO)
Cellulase + amylase UV + mixture of enzymes
69.11 69.09
68.37 68.55
68.21 70.45
68.22 72.40
Printed and non-treated paper brightness (%ISO) Printed and non-treated paper dirt area (%)
68.89 71.41
68.22 71.44
Average (%ISO)
Dirt area (%)
68.50 70.56
0.38 0.02
62.35 0.60
Conditions: enzymes processing time 30 min; enzymes temperature 40 ◦ C; UV time 1 min; pulp concentration 4% (w/w); the cellulase concentration of 0.06% (w/w) was selected for treating 8 g of dry pulp sample; the amylase concentration of 0.088% (w/w) was selected for treating 8 g of dry pulp sample; printed and non-treated papers sample was the pulp sample not treated with enzyme and also not processed by UV and flotation.
particles very difficult to be peeled off from fibers. Therefore, it is a problem desiderated to be solved in de-inking technology. UV can initiate degradation of polymers or even break it into pulverization. For this reason, the actions of laser printing paper irradiated by ultraviolet have been investigated (see Figs. 2 and 3 and Table 4). According to Section 2.4 (Technology (d)), the combine deinking technology of UV radiation and mixture of enzymes was experimented and compared it with mixture enzymes de-inking technology. Table 4 shows UV can improve brightness of pulp in some degree and reduce dirt area obviously. From Fig. 2, we can see when irradiation time is 0–1 min by 1000 W UV lamp, brightness rise and dirt area descend. The reason may be that thermosetting resin is partly decomposed by UV irradiation which makes the particles loosen, and then the toner particles are easy to be removed during flotation and water washing. Brightness fall gradually and the change of dirt area is little when irradiation time is 2–5 min. The phenomenon can be explained by the reason that paper becomes yellow with the time increasing of UV irradiation. Therefore considering brightness and dirt area, the appropriate UV irradiation time is 1 min or lower than 1 min. For observing the breakage action of ultraviolet irradiation to printed paper, big toner points were printed on the paper and they were irradiated by ultraviolet for different time respectively (see Fig. 3). From Fig. 3, we can see that the toner on fibers was distinctly tilted when irradiation time changed from 1 min (enclosing part of Fig. 3a), 2 min (Fig. 3b) to 4 min (Fig. 3c). It indicates ultraviolet irradiation is useful for de-inking. Otherwise, from Section 2.4 (Technology (d)), we know that the combined de-inking technology of UV irradiation and enzymes does not needed the preprocess with alkali, therefore, it is a environment-friendly de-inking technology.
Fig. 3. Photos of scanning electron microscopy (SEM) of different irradiation time.
Fig. 2. Influence of UV irradiation time on brightness and dirt area. Conditions: enzymes processing time 30 min; enzyme processing temperature 40 ◦ C; pulp mass concentration 4% (w/w); the cellulase concentration of 0.06% (w/w) was selected for treating 8 g of dry pulp sample; the amylase concentration of 0.088% (w/w) was selected for treating 8 g of dry pulp sample.
4. Conclusion The effect of combined de-inking technology of ultrasonic, UV irradiation and enzyme on HP laser printed paper has been investi-
S. Zhenying et al. / Chemical Engineering and Processing 48 (2009) 587–591
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